Some effects of Veronese map on syzygies of projective varieties

Abstract

Let $X \subset \P^r$ be a nondegenerate projective variety and let $\nu_{\ell} : \P^r \to \P^N$ be the $\ell$-th Veronese embedding. In this paper we study the higher normality, defining equations and syzygies among them for the projective embedding $\nu_{\ell} (X) \subset \P^N$. We obtain that for a very ample line bundle $L \in {Pic}X$ such that $X \subset \P H^0 (X,L)$ is $m$-regular in the sense of Castelnuovo-Mumford, $(X,L^{\ell})$ satisfies property $N_{\ell}$ for all $\ell \geq m$ (Theorem \ref{thm:main1}). This is a generalization of M. Green's work that $(\P^r,\mathcal{O}_{\P^r} (\ell))$ satisfies property $N_{\ell}$. Also our result refines works of Ein-Lazarsfeld in \cite{EL}, Gallego-Purnaprajna in \cite{GP} and E. Rubei in \cite{Rubei1}, \cite{Rubei} and \cite{Ru1}.